Resonance Raman investigation of the electronic transitions of some iron(II) and copper(II)α-di-imine complexes

Abstract

The electronic, i.r., Raman, and resonance Raman spectra of [Fe(phen)₂(CN)₂](phen = 1,10-phenanthroline), [Cu(bq)Br₂](bq = 2,2′-biquinolyl), and [Fe(bipy)₃][BF₄]₂(bipy = 2,2′-bipyridyl) have been studied. Excitation within the contours of the strong visible charge-transfer bands in the electronic spectra of these complexes leads to the resonance enhancement of many of the a₁ modes of the α-di-imine ligands. The electronic shoulders (present for all three complexes) have their origin in vibronic coupling for [Fe(bipy)₃][BF₄]₂ and [Cu(bq)Br₂]. The electronic side-band for [Fe(phen)₂(CN)₂], however, arises from a second electronic transition. The presence of more than one ν(CN) mode in the Raman spectrum of [Fe(phen)₂(CN)₂] dissolved in 1 mol dm^–3 H₂SO₄ has been explained in terms of protonation of the phenanthroline ligand.